Bearer traffic in a switched telephone network may be characterized as intra-office traffic, inter-office traffic and inter-exchange traffic. Intra-office traffic is traffic that originates and terminates in an end office. Inter-office traffic is traffic that originates in one end office and terminates in another end office in the same exchange. Inter-office traffic may be routed directly between end offices on trunks referred to as "high usage group" trunks, or indirectly through a local tandem switch. Inter-exchange traffic is traffic that originates in an end office in one exchange, and terminates in an end office in another exchange. Inter-exchange traffic is routed through one or more tandem switches before it reaches a terminating end office.
In a conventional switched telephone network, switches are arranged heirarchically and are interconnected by trunks used to complete calls. The hierarchical structure of the network minimizes the number of trunks required to provide full connectivity in the network. Nonetheless, in order to ensure adequate capacity and routing flexibility, a large number of trunk groups must be terminated at each switch in the network. It is well known that each trunk group requires maintenance of the physical facilities, as well as maintenance of the routing and translation tables required for call routing. Consequently, whenever a new trunk or trunk group has to be provisioned between switches, the routing tables at each of the switches must be updated so that calls can be routed over these newly provisioned trunks. Conversely, if a trunk or trunk group has to be de-commissioned for maintenance, both of the switches connected to the trunk group must have their routing tables updated to prevent calls from being routed over those trunks.
In recent years, the volume of traffic in the Public Switched Telephone Network (PSTN) has increased dramatically as a result of new telephone services and the increased demand for access to Internet Service Providers (ISPs). This increase in traffic volume has necessitated an increase in the number of trunks provisioned between switches in the PSTN. Concurrently, the introduction of competition in most telephone service markets has forced service providers to examine operating costs in an effort to become more competitive. The examination of operating costs has revealed that operating costs associated with trunk provisioning and maintenance contribute significantly to operating overhead. Consequently, a need exists for a way of controlling the operating overhead associated with trunk provisioning at each of the switches in a switched telephone network.
There has been considerable recent interest in the use of asynchronous transfer mode (ATM) backbone networks for the transfer of switched telephone traffic to increase network capacity. Several different systems for accomplishing this have been invented, including Applicant's co-pending application, entitled TRANSIT TRUNK SUBNETWORK, filed Sep. 23, 1998, and assigned application Ser. No. 09/158,855. A transit trunk subnetwork has several distinct advantages over conventional inter-switch trunk facilities when utilized as described in the above-referenced patent application. For example, the ATM backbone resources in the network can be used to permit flexible routing options between originating and terminating end offices in the switched telephone network. This substantially eliminates the heirarchical structure of the switched telephone network and permits dynamic resource sharing. During low usage periods, the ATM backbone resources can be used for other purposes, such as data transfer to other networks, to further increase revenue and offset operating costs. However, in order to fully capitalize on the benefits offered by the transit trunk subnetwork, there exists a need for a mechanism that permits flexible routing, while minimizing the overhead costs associated with trunk maintenance.